CUDA Error in Cycles on a Mac
I have the same issue on a Mac Pro 5,1 using an Nvidia 980GTX with 4gb of ram. It'll CUDA error on a simple scene sometimes. 

• What I can find help is to shut all other apps down reopen Blender and try again.

• Reboot, only open blender and try again

• I use a 4k monitor, sometimes, halving the resolution can make it work. 

I think it's a known error, that I really hope it's something that's addressed in the future. 

Is this only mac users or do windows / linux users suffer the same problem? I might make a bootcamp or linux partition if there's no issues there.